Method for cleaning electrodes



May 22, 1956 E. B. CHAPMAN 2,745,831

METHOD FOR CLEANING ELECTRODES Filed Aug. 27. 1952 FIG. I FIG. 2

l |2sl| I25 H I] I H I II II I0 l0 INVENTOR EDWARD B. CHAPMAN ATTORNEYUnited States Patent METHOD FOR CLEANING ELECTRODES Edward B. Chapman,Poughkeepsie, N. Y., assignor to International Business MachinesCorporation, New York, N. Y., a corporation of New York ApplicationAugust 27, 1952, Serial No. 306,554

4 Claims. (Cl. 316--26) This invention relates to electron tubes andmore particularly to a novel means and method for removing theimpurities from the electrodes of tubes.

In gaseous discharge tubes impurities are usually present in themetallic electrode structure used. These impurities may shorten theuseful operable life of the tubes. Also, the presence of impuritiescauses tubes to have a relatively high internal resistance and requiresa relatively high R. F. voltage to effect a firing of the tubes or adeionization of the gaseous atmosphere within the tubes.

Accordingly, it is an object of the present invention to provide a novelmeans and method for eliminating the impurities present in the electrodestructure of a tube.

Another object is to utilize heating and cooling means for eliminatingimpurities present in the metallic electrode structure of a tube.

A further object is to provide a novel method of removing the impuritiesfrom the electrodes of a gaseous discharge tube which method includesvaporizing a portion of the metallic electrode structure including theimpurities and depositing the same upon the envelope of the tube,subsequently vaporizing the electrode metal deposited upon the envelopeand redepositing it upon the same electrodes of the tube.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of examples, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is an elevation view of a gaseous discharge tube showing meansfor heating the electrodes,

' Fig. 2 is an elevation view of the tube shown in Fig. 1 wherein thetube has been rotated 90 about its longitudinal axis, and

Fig. 3 is a cross-sectional view along line a-a of Fig. 1.

The novel method of the invention will be explained by way of examplewith specific reference to its use in connection with a gaseousdischarge diode. In such a tube impurities in the electrode structureare especially objectionable in that they cause short tube life becauseof the influence of the impurities upon the ionization and deionizationof the gaseous atmosphere within the tube.

Briefly, in the practice of the invention the electrode supports of atube may be of any suitable type or form such as a wire type nickelalloy. A thin-walled aluminum sleeve is placed over each of theseelectrode supports. These sleeves serve as the normal operableelectrodes of the tube and the usual impurities must be removed fromthem in order to realize optimum tube operation. Among these impurities,for example, is magnesium, aluminum oxide, occluded gases and dirt.These impurities along with aluminum from the surface of the sleeves arevaporized and partly deposited upon the relatively cool envelope of thetube. The aluminum on the envelope is then vaporized and deposited uponthe electrodes. As a result, the surface of the electrodes issubstantially free of any contact of the auto transformer AT, to thealuminum ice 2 impurities which adversely affect the operation of thetube.

Referring more particularly to the drawings, the electrode supports 10and 11 are supported by a standard press seal 12s. The aluminum sleeves12 and 13 are placed over the electrode supports 10 and 11,respectively. These sleeves are contained within the glass envelope 14which is filled with any suitable gaseous atmosphere. A conductive band15 is placed around the envelope 14 as shown. If it is desired to ionizeand deionize the tube in response to a change of R. F. voltage, such isaccomplished by applying that voltage to the band 15. This band may beof any suitable type and does not constitute part of this invention. Forexample, a band may be formed from painting the envelope with conductivesilver paint to form an annular ring therearound approximately .002 inchin thickness. t

The actual spacing and size of the electrode supports is not critical inthe performance of the invention. It is merely required that thesesupports be more heat resistant than the aluminum sleeves 12 and 13placed thereover. As an example the electrode supports may be .020 inchin diameter and spaced .025 inch apart. The outer diameter of thealuminum sleeve may be .030 inch and the inner diameter of anyappropriate size to be received by the electrode supports. The outsidediameter of the glass envelope may be approximately 8 millimeters and ofstand ard wall thickness.

The winding of an auto transformer AT is connected to the terminals of avolt A. C. supply and its output is connected to the primary winding pof a transformer T having one end of its secondary Winding s connectedto electrode support 10. The other end of the winding s is sleeves 12and 13 as required for carrying out the inven tion. The impurities areremoved from the electrodes after they are placed in the envelope andbefore the envelope is sealed or the tip-off 17 is formed.

First, the envelope is evacuated and is heated by means of an oven ortorch to a temperature below that which will effect a softening of theglass, that is, below approximately 300 C. This heat effects a cleaningof the glass and liberates occluded gases from the glass. The gases thusliberated are then pumped out of or evacuated from the envelope.

After evacuation of the liberated gases is effected the pump orevacuating means is rendered ineffective and neon is admitted into theenvelope until a pressure of 10 to 15 millimeters of Hg is obtained. Thetransformer T and the auto transformer AT are now utilized to apply 200to 250 volts A. C. across the electrode supports 10 and 11 to effect anionization of the neon between the sleeves 12 and 13. If this voltage isapplied for approximately two minutes the aluminum sleeves become veryhot and the glass envelope is at a lower temperature. At this time thetemperature of the electrodes and the envelope are substantially stableand each approach a state of thermal equilibrium. The voltage applied tothe electrode supports is now increased to approximately 300 volts. Thiscauses impurities present in the aluminum sleeves 12 and 13 and aportion of the aluminum of the sleeves to be vaporized and depositedupon the surface of the relatively cool glass envelope. This vaporizingis indicated by a purple glow discharge between the aluminum sleeves andis terminated by manipulation of the arm of transformer AT when asubstantially solid sheet of aluminum appears on the walls of theenvelope.

The above described heating and vaporizing may also be accomplished byany gradual heating of the aluminum sleeves which causes thevaporization to take place.

The envelope is again evacuated. The neon previously placed in the tubeand the occluded gases liberated by the vaporization are removed.

Evacuation of the envelope is continued. The glass envelope of the tubeis again baked or heated. This causes most of the aluminum present onthe envelope to be vaporized and to return to the relatively coolaluminum sleeves 12 and 13. Most of the impurities remain on the glass.

Evacuation is continued until the desired vacuum is attained and then itis stopped. The desired gas is admitted, for example, 2 millimeters ofargon, then millimeters of neon. The tube is then tipped off or closed.An A. C. voltage is again applied to the electrode supports it} and 11to effect ionization of the gas all along the aluminum sleeves 12 and 13to thereby effect an aging or oreopera tional conditioning of the tubein a usual manner.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in theart, without departing from the spirit of the invention. it is theintention, therefore, to be limited only as indicated by the scope ofthe following claims.

What is claimed is:

1. In the manufacture of a gaseous discharge tube having at least twometallic electrodes to be enclosed in an outer envelope the process ofeliminating impurities from the electrodes including the followingstepsfevacuating said envelope while heating said envelope to atemperature less than the melting point thereof to thereby effect acleaning thereof and liberation of occluded gases therefrom; injectingneon into said tube until a predetermined pressure is realized; applyingan alternating current voltage of between 200 and 250 volts across saidelectrodes to ionize said neon until the temperature of said electrodesand said envelope approach a state of substantial thermal equilibrium;increasing the voltage across said electrodes to approximately 360 voltsto vaporize metallic particles and impurities from said electrodes untila substantially opaque metallic sheet is deposited upon said envelope;evacuating said envelope to remove said neon and occluded gasestherefrom and heating said envelope to evaporate metallic particlestherefrom and deposit them upon the surface of said electrodes therebyproviding a substantially pure metallic surface upon the electrodes.

2. The process set forth in claim 1 wherein said electrodes includealuminum sleeves supported upon electrode supports made of a nickelalloy and said envelope is made of glass.

3. In the manufacture of a gaseous discharge tube having at least twoaluminum electrodes to be enclosed in an outer glass envelope theprocess of eliminating impurities from the electrodes which includes thefollowing steps; evacuating said envelope while heating said envelope toa temperature less than the melting point thereof to thereby effect acleaning thereof and liberation of occluded gases therefrom; injectingneon into said envelope until a predetermined pressure is realized;applying A. C. voltage of between 200 and 250 volts across saidelectrodes to ionize said neon until the temperature of said electrodesand said envelope approach a state of thermal equilibrium; applying heatto said electrodes to vaporize aluminum particles and impurities fromsaid electrodes until a substantially opaque aluminum sheet is depositedupon said envelope; evacuating said envelope to remove said neon andoccluded gases therefrom and heating said envelope to evaporate aluminumparticles therefrom and deposit them upon the surface of said electrodesthereby providing a substantially pure metallic surface upon theelectrodes.

4. In the manufacture of a gaseous discharge tube having at least twometal electrodes to be enclosed in an outer glass envelope the processof eliminating impurities from the electrodes which includes thefollowing steps: evacuating said envelope while heating said envelope toa temperature less than the melting point thereof to thereby effect acleaning thereof and liberation of occluded gases therefrom; injectingan inert gas into said envelope until a predetermined pressure isrealized; applying an alternating current voltage of between 200 and 250volts across.

said electrodes to ionize said inert gas until the temperature of saidelectrodes and said envelope approach a state of thermal equilibrium;applying heat to said electrodes to vaporize metal particles andimpurities from said electrodes until a substantially opaque metal sheetis deposited upon said envelope; evacuating said envelope to remove saidinert gas and occluded gases therefrom and heating said envelope toevaporate metal particles therefrom and deposit them upon the surface ofsaid electrodes thereby providing a substantially pure metallic surfaceupon the electrodes.

References Cited in the file of this patent UNITED STATES PATENTS1,927,812 Thomson Sept. 19, 1933 2,401,734 lanes June ll, 1946 2,467,953Bancroft et al Apr. 19, 1949 2,591,474 Stutsman Apr. 1, 1952

1. IN THE MANUFACTURE OF A GASEOUS DISCHARGE TUBE HAVING AT LEAST TWOMETALLIC ELECTRODES TO BE ENCLOSED IN AN OUTER ENVELOPE THE PROCESS OFELIMINATING IMPURITIES FROM THE ELECTRODES INCLUDING THE FOLLOWINGSTEPS; EVACUATING SAID ENVELOPE WHILE HEATING SAID ENVELOPE TO ATEMPERATURE LESS THAN THE MELTING POINT THEREOF TO THEREBY EFFECT ACLEANING THEREOF AND LIBERATION OF OCCLUDED GASES THEREFROM; INJECTINGNEON INTO SAID TUBE UNTIL A PREDETERMINED PRESSURE IS REALIZED; APPLYINGAN ALTERNATING CURRENT VOLTAGE OF BETWEEN 200 AND 250 VOLTS ACROSS SAIDELECTRODES TO IONIZE SAID NEON UNTIL THE TEMPERATURE OF SAID ELECTRODEAND SAID ENVELOPE APPROACH A STATE OF SUBSTANTIAL THERMAL